The first units of KFOR entered Kosovo on 12 June 1999, finding devastation throughout Hundreds of thousands of refugees living in the surrounding countries of Macedonia, Albania and Montenegro were returning to their homes, which had to be cleared from mines. Tens of thousands of houses had to be rebuilt.

At the same time, thousands of armed former members of the ethnic Albanian Kosovo Liberation Army (KLA) gained political control over their home municipalities, perceiving themselves the saviours of Kosovo. KFOR also had to protect Kosovo Serbs, as factions of the former KLA had begun driving them from their homes throughout Kosovo, thus creating a second humanitarian crisis.

The KLA was later disbanded and transformed into a 3,000 strong Kosovo Protection Corps under KFOR supervision.

KFOR faced its darkest days in March 2004, with the eruption of riots targeting both the UN and Kosovo Serbs. The reaction of the international troops was strongly criticized.

KFOR initially numbered some 50,000 personnel. Three contingents – the British, Canadian, and Russian, all of which had accounted for a large number of KFOR troops – have since left Kosovo. Other nations with smaller contingents followed, while France, the United States and Germany reduced their forces. By 2002, KFOR had been reduced to around 39,000 troops; and to around 26,000 by June 2003. Numbers continued to fall since; KFOR is now said to number about 15,000 troops.